Superdeterminism and the Mermin Device

[PeterDonis]

What you need to show is an example where a conservation law was VIOLATED when the observation is made.

No, you need to show that a conservation law must be violated if the universe is not fully 100% deterministic because you are the one who is making that claim. I am simply pointing out that you have not shown that. You have simply assumed it, and you can't just assume it. You have to show it.

The rest of your post is irrelevant to mine because I did not say any of the things you are talking about.

 

[PeterDonis]

Speculating that every time a “measurement” is made a new Universe comes into existence.

This is not what the MWI says. The "universe" in the MWI is the universal wave function, and there is always just one universal wave function. The wave function doesn't "split" when a measurement is made; that would violate unitary evolution, and the MWI says that the wave function always evolves in time by unitary evolution.

 

[PeterDonis]

a deterministic Universe we have give up free will for

You are aware that the MWI is 100% deterministic, correct?

 

[Lord Jestocost]

I am not refuting you statements, but there are Physicists who believe SD is viable, including Bell himself.

At the last resort, “questions of faith” are irrelevant for doing physics. All one needs to carry out physics are observations that can be used to construct and test models – on the basis of the observed phenomena.

 

[RUTA]

I don't think this claim can be asserted as fact at our current level of knowledge. When we make measurements on quantum systems, we bring into play huge sinks of energy and momentum (measuring devices and environments). But we don't measure the change in energy and momentum of the sinks. We only look at the measured systems. But if a measurement takes place, the measured systems are not closed systems and we should not in general expect them to obey conservation laws in isolation; they can exchange energy and momentum with measuring devices and environments. To know that conservation laws were violated we would have to include the changes in energy and momentum of the measuring devices and environments. But we don't. So I don't see that we have any basis to assert what you assert in the above quote. All we can say is that we have no way of testing conservation laws for such cases at our current level of technology.

My claim is a mathematical fact that follows from the Bell state formalism alone. It has nothing to do with experimental uncertainty.

 

[PeterDonis]

My claim is a mathematical fact that follows from the Bell state formalism alone.

As I said, this can't be correct because during the measurement process angular momentum is exchanged between the measured particles, which the formalism you refer to describes, and the measuring devices and environment, which the formalism does not describe. So the formalism is incomplete and cannot support any claims about conservation laws.

It has nothing to do with experimental uncertainty.

My point has nothing to do with experimental uncertainty. It has to do with the fact that during measurement, the measured particles are open systems, not closed systems.

 

[RUTA]

As I said, this can't be correct because during the measurement process angular momentum is exchanged between the measured particles, which the formalism you refer to describes, and the measuring devices and environment, which the formalism does not describe. So the formalism is incomplete and cannot support any claims about conservation laws.My point has nothing to do with experimental uncertainty. It has to do with the fact that during measurement, the measured particles are open systems, not closed systems.

Look at a Bell spin triplet state in the symmetry plane. When Alice and Bob both measure in the same direction, they both get the same outcome, +1 or -1. That is due to conservation of spin angular momentum. Now suppose Bob measures at an angle $\theta$ with respect to Alice and they do many trials of the experiment. When Alice partitions the data according to her +1 or -1 results, she expects Bob to measure $+\cos{\theta}$ or $-\cos{\theta}$, respectively, because she knows he would have also measured +1 or -1 if he had measured in her direction. Therefore, she knows his true, underlying value of spin angular momentum is +1 or -1 along her measurement direction, so he should be measuring the projection of that true, underlying value along his measurement direction at $\theta$ to conserve spin angular momentum. Of course, Bob can partition the data according to his $\pm 1$ equivalence relation and say it is Alice who should be measuring $\pm \cos{\theta}$ in order to conserve spin angular momentum. It is impossible to conserve spin angular momentum exactly according to either Alice or Bob because they both always measure $\pm 1$ (in accord with the relativity principle), never a fraction. However, their results do average $\pm \cos{\theta}$ under these data partitions. It has nothing to do with momentum transfer with the measurement device. All of this follows strictly from the Bell spin state formalism.

 

[PeterDonis]

It is impossible to conserve spin angular momentum exactly according to either Alice or Bob because they both always measure $\pm 1$ (in accord with the relativity principle), never a fraction. However, their results do average $\pm \cos{\theta}$ under these data partitions. It has nothing to do with momentum transfer with the measurement device.

Sorry, these statements are simply false as a matter of what actually happens in an experiment. Measurement involves interaction between the measured system and the measuring device. That interaction can exchange conserved quantities. So it is simply physically invalid to only look at the measured systems when evaluating conservation laws.

 

[RUTA]

Sorry, these statements are simply false as a matter of what actually happens in an experiment. Measurement involves interaction between the measured system and the measuring device. That interaction can exchange conserved quantities. So it is simply physically invalid to only look at the measured systems when evaluating conservation laws.

The Bell spin states obtain due to conservation of spin angular momentum without regard to any loss to the environment. Therefore, the theoretical results I shared are independent of experimental uncertainties, which is what you're trying to invoke.

 

[PeterDonis]

The Bell spin states obtain due to conservation of spin angular momentum without regard to any loss to the environment.

How do you know? You're not measuring the exchange of angular momentum with the environment. That doesn't mean you can assume it doesn't happen. It means you don't know.

the theoretical results I shared are independent of experimental uncertainties, which is what you're trying to invoke.

I don't know where you're getting this from. There can't be any experimental uncertainty in something that's not being measured. The fact that measurement involves interaction between the measured system and the measuring device is basic QM. But it does not imply that all aspects of that interaction are captured in the measurement result. In fact they practically never are.

 

[vanhees71]

Sorry, these statements are simply false as a matter of what actually happens in an experiment. Measurement involves interaction between the measured system and the measuring device. That interaction can exchange conserved quantities. So it is simply physically invalid to only look at the measured systems when evaluating conservation laws.

I don't know, how often we have discussed these wrong statements in the forum. Should this really be part of the Insights?

 

[PeterDonis]

Should this really be part of the Insights?

I don't know. The point I have made is not one I have seen addressed in the literature. But that doesn't make it wrong.

 

[Lord Jestocost]

How do you know? You're not measuring the exchange of angular momentum with the environment. That doesn't mean you can assume it doesn't happen. It means you don't know.

If a particle's spin is "measured" along a certain axis, it will "exhibit" spin that corresponds to a vector parallel to the axis of measurement. The question is: Does a quantum spin "exhibition" actually impart quantum spin to the surroundings?

 

[PeterDonis]

The question is: Does a quantum spin "exhibition" actually impart quantum spin to the surroundings?

"Impart quantum spin" is too narrow; it should be "exchange angular momentum". Quantum spin can be inter-converted with other forms of angular momentum.

I would be interested in seeing any references in the literature to analyses of measurement interactions that address this question.

 

[vanhees71]

I don't know. The point I have made is not one I have seen addressed in the literature. But that doesn't make it wrong.

I didn't mean that you are wrong but the statements by @RUTA . We had extended discussions about this repeatedly!

 

[PeterDonis]

I didn't mean that you are wrong but the statements by @RUTA . We had extended discussions about this repeatedly!

Can you give any links to threads/posts?

 

[Lord Jestocost]

"Impart quantum spin" is too narrow; it should be "exchange angular momentum". Quantum spin can be inter-converted with other forms of angular momentum.

I would be interested in seeing any references in the literature to analyses of measurement interactions that address this question.

To my mind, you find some thoughts on MathPages in the article “On Cumulative Results of Quantum Measurements”.
https://www.mathpages.com/home/kmath419/kmath419.htm

 

[vanhees71]

Here's the most detailed discussion about this misleading statements on angular-momentum conservation in QT of mine I could find, using the search function:

https://www.physicsforums.com/threa...elers-1986-paper-comments.952665/post-6056948

 

[RUTA]

How do you know? You're not measuring the exchange of angular momentum with the environment. That doesn't mean you can assume it doesn't happen. It means you don't know.

The Bell spin states are chosen to model conserved spin angular momentum. It's totally analogous to having an astronaut throw her flashlight in outer space so that conservation of momentum makes her move toward her spaceship. You write $\vec{P}_{astronaut} + \vec{P}_{flashlight} = 0$. Of course if you wanted to confirm this you'd have to make measurements and that would introduce experimental uncertainty because momentum would be lost relative to the equation. But, that is not conveyed in the equation itself.

 

[PeterDonis]

To my mind, you find some thoughts on MathPages in the article “On Cumulative Results of Quantum Measurements”.
https://www.mathpages.com/home/kmath419/kmath419.htm

This article doesn't talk at all about what I was talking about, namely, the exchange of conserved quantities (such as angular momentum) between measured systems and measuring devices (and environments).

 

[PeterDonis]

The Bell spin states are chosen to model conserved spin angular momentum if you ignore any exchange of angular momentum between the measured systems and measuring devices and environments, and if you ignore that spin angular momentum is not the same as total angular momentum.

See the bolded qualifier I added. My point is that you can't ignore what is being ignored in the definition of the Bell spin states, if you are going to make claims about conservation laws. Conservation laws don't apply to open systems in isolation. They also don't apply to particular pieces of a conserved quantity in isolation. Spin angular momentum is not conserved by itself; only total angular momentum is conserved. But only spin angular momentum of the measured particles is captured in the mathematical model using Bell states.

 

[RUTA]

I didn't mean that you are wrong but the statements by @RUTA . We had extended discussions about this repeatedly!

And as I explained to you in those discussions, everything I am saying follows mathematically from the Bell states. There is absolutely nothing wrong with my statements. That's why it's been published numerous times in various contexts now. I have no idea what confuses you about it, so I can't help you there. Sorry.

 

[PeterDonis]

everything I am saying follows mathematically from the Bell states

Only if you assume that angular momentum conservation can be applied to the combined spin angular momentum of the measured systems taken in isolation, even though they are open systems during measurement and even though spin angular momentum is not conserved separately. But that assumption is false.

 

[RUTA]

See the bolded qualifier I added. My point is that you can't ignore what is being ignored in the definition of the Bell spin states, if you are going to make claims about conservation laws. Conservation laws don't apply to open systems in isolation. They also don't apply to particular pieces of a conserved quantity in isolation. Spin angular momentum is not conserved by itself; only total angular momentum is conserved. But only spin angular momentum of the measured particles is captured in the mathematical model using Bell states.

The bolded statement is exactly correct, assuming no losses to the measurement device. Such losses would vary from situation to situation even though the source of spin-entangled particles was the same in every experimental arrangement. Therefore, the Bell spin states certainly do not attempt to capture such losses, as they are not written in a form where one can enter specific experimental details.

 

[RUTA]

Only if you assume that angular momentum conservation can be applied to the combined spin angular momentum of the measured systems taken in isolation, even though they are open systems during measurement and even though spin angular momentum is not conserved separately. But that assumption is false.

See post #114

 

[PeterDonis]

the Bell spin states certainly do not attempt to capture such losses

Which means you cannot use them as a basis for claims about conservation laws.

Such losses would vary from situation to situation

This is much too vague. I would say that the exchange of angular momentum between the measured particle and the measuring device would vary based on the orientation of the measuring device. Which is precisely the kind of variation that could maintain conservation of total angular momentum in cases where the two entangled particles have their spins measured in different orientations.

 

[RUTA]

Which means you cannot use them as a basis for claims about conservation laws.

Is that what you would say about the astronaut?

This is much too vague. I would say that the exchange of angular momentum between the measured particle and the measuring device would vary based on the orientation of the measuring device. Which is precisely the kind of variation that could maintain conservation of total angular momentum in cases where the two entangled particles have their spins measured in different orientations.

Now it looks like you want to invoke counterfactual definiteness for the particles' spins (like Alice and Bob in my story). The reason I do that is precisely to show how it differs from the QM prediction of $\pm 1$ at all angles. How would your explanation account for the $\pm 1$ prediction at all angles, given it is supposedly accounting for transfer to the environment, which would certainly vary with angle.

 

[PeterDonis]

Is that what you would say about the astronaut?

What astronaut?

Now it looks like you want to invoke counterfactual definiteness for the particles' spins

I don't know where you are getting that from. I am only talking about the spin measurement results that are actually observed, not about any counterfactual ones.

How would your explanation account for the $\pm 1$ prediction at all angles

The $\pm 1$ prediction at all angles means that the net angular momentum exchange between the measured particles and the measuring devices (i.e., the vector sum of the exchanges from both measurements) must vary by angle (more precisely, by the difference in angle between the two measurements) if total angular momentum is to be conserved. (Note that the angular momentum that is exchanged does not have to be spin; it can be orbital, since what needs to be conserved is total angular momentum, not spin alone.) And that is what we would expect since we expect the angular momentum vector describing the exchange in each individual measurement to vary with the orientation of the measuring device.

 

[DrChinese]

So we do need to find a valid theory that works. Sean Carrol advocates for the “many worlds” interpretation. ... But I have to believe that, since there are legitimate scientists who believe SD is a possible reality, that it is a least POSSIBLE a theory can be developed. It just seems odd that most of the arguments I have read by Physicists against SD are emotional opinionated arguments dealing with free will, and “many worlds” is considered over SD as a better alternative, but Bell recognizing SD as a possible loophole to his theorem. Did he just not think it through before he made that statement? Is there something in the points that you make above the John Bell was not aware of? Specifically something that has been discovered after Bell that invalidates his claim?

1. I won't defend MWI, you can see the reasoning in favor of it in papers about it. I think an honest assessment will admit it is viable, and as best I understand it there is no net creation of matter/energy involved regardless of the number of worlds. But I could be wrong.2. I am not sure what you mean about "emotional arguments", but for SD to work as a local realistic solution:

There must be a locally accessible "master plan" particle/field/property/object that instructs each quantum interaction how to act (i.e. to provide the outcome of every measurement). This master plan would have object copies in every region of space (to be local), and must provide "answers" (measurement outcomes) for at least 13.8 billion years of history of particles/energy being created/destroyed/transformed, etc. And it must do so in a manner so that the "true" quantum statistics (to explain Bell's result) are hidden from inquiring human experimentalists investigating Quantum Theory, which provides an accurate prediction of the observed statistics.

Really, I don't know where one starts to develop this from "handwaving speculation" to a credible hypothesis or theory. But I guess it is "possible" someone might do so in the future, in which case we would have something to critique (or perhaps test, although that is not really a requirement for an interpretation). As it is now, SD is impossible to critique precisely because its supporters give it such amazing elements/powers - of course constructed on the fly - that no criticism can topple it. This is no different than invoking the existence of an omniscient omnipotent deity, by the way. 3. Bell was not a believer in Superdeterminism. Like most, he threw that out to demonstrate how far you would need to go to keep local realism (post Bell's Theorem). He didn't need to come up with any details, leaving it to the audience to draw their own conclusions. (He could just as easily have invoked the above deity making the same decisions.)

Bell (1985ish): "There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the "decision" by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster than light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already "knows" what that measurement, and its outcome, will be."

Unsaid: what created the original map (master plan); and how did it calculate, store and hide all of the future outcomes? How does an entangled particle know how to read the map so it can acquire the proper spin (when spin correlations are being studied in a lab)?

 

[StevieTNZ]

What astronaut?

https://www.physicsforums.com/threads/superdeterminism-and-the-mermin-device.1013414/post-6818631